Fix deprecation messages caused by recent changes to Duration.

Yeah, some of the pieces were sensible in and of themselves but didn't fit as well in the whole (like `FracSec`), and some of the pieces made some sense with regards to the whole but were too confusing on their own (like having the individual getters on `Duration` giving the split rather than the total).

I'll have to think this through a bit to decide what the best thing to do about `FracSec` is - maybe have something like `sysTime.fracSec!"msecs"`? I don't know. Ideally, whatever we end up with would be simpler and less verbose than what we have now without adding a different type of confusion. The number of places in date/time stuff that are very similar but not quite the same makes it distressingly easy to come up with an API that's going to confuse people and annoyingly difficult to come up with one that's truly consistent.